[Settings] Use a settings applicator to set the default TFTP URI.

src/include/gpxe/dhcp.h

 extern void delete_dhcp_option ( struct dhcp_option_block *options,
 				 unsigned int tag );
 
-extern int apply_dhcp_options ( struct dhcp_option_block *options );
-extern int apply_global_dhcp_options ( void );
-
 extern int create_dhcp_request ( struct net_device *netdev, int msgtype,
 				 struct dhcp_option_block *options,
 				 void *data, size_t max_len,

src/net/dhcpopts.c

 	dhcpopt_get ( options );
 	list_add_tail ( &options->list, &existing->list );
 
-	/* Apply all registered DHCP options */
-	apply_global_dhcp_options();
 }
 
 /**
 			  unsigned int tag ) {
 	set_dhcp_option ( options, tag, NULL, 0 );
 }
-
-/**
- * Apply DHCP options
- *
- * @v options		DHCP options block, or NULL
- * @ret rc		Return status code
- */
-int apply_dhcp_options ( struct dhcp_option_block *options ) {
-	struct in_addr tftp_server;
-	struct uri *uri;
-	char uri_string[32];
-
-	/* Set current working URI based on TFTP server */
-	find_dhcp_ipv4_option ( options, DHCP_EB_SIADDR, &tftp_server );
-	snprintf ( uri_string, sizeof ( uri_string ),
-		   "tftp://%s/", inet_ntoa ( tftp_server ) );
-	uri = parse_uri ( uri_string );
-	if ( ! uri )
-		return -ENOMEM;
-	churi ( uri );
-	uri_put ( uri );
-
-	return 0;
-}
-
-/**
- * Apply global DHCP options
- *
- * @ret rc		Return status code
- */
-int apply_global_dhcp_options ( void ) {
-	return apply_dhcp_options ( NULL );
-}

src/net/udp/tftp.c

 #include <gpxe/retry.h>
 #include <gpxe/features.h>
 #include <gpxe/bitmap.h>
+#include <gpxe/settings.h>
+#include <gpxe/dhcp.h>
+#include <gpxe/uri.h>
 #include <gpxe/tftp.h>
 
 /** @file
 	.scheme	= "mtftp",
 	.open	= mtftp_open,
 };
+
+/**
+ * Apply TFTP configuration settings
+ *
+ * @ret rc		Return status code
+ */
+static int tftp_apply_settings ( void ) {
+	static struct in_addr tftp_server = { 0 };
+	struct in_addr last_tftp_server;
+	char uri_string[32];
+	struct uri *uri;
+
+	/* Retrieve TFTP server setting */
+	last_tftp_server = tftp_server;
+	fetch_ipv4_setting ( NULL, DHCP_EB_SIADDR, &tftp_server );
+
+	/* If TFTP server setting has changed, set the current working
+	 * URI to match.  Do it only when the TFTP server has changed
+	 * to try to minimise surprises to the user, who probably
+	 * won't expect the CWURI to change just because they updated
+	 * an unrelated setting and triggered all the settings
+	 * applicators.
+	 */
+	if ( tftp_server.s_addr != last_tftp_server.s_addr ) {
+		snprintf ( uri_string, sizeof ( uri_string ),
+			   "tftp://%s/", inet_ntoa ( tftp_server ) );
+		uri = parse_uri ( uri_string );
+		if ( ! uri )
+			return -ENOMEM;
+		churi ( uri );
+		uri_put ( uri );
+	}
+
+	return 0;
+}
+
+/** TFTP settings applicator */
+struct settings_applicator tftp_settings_applicator __settings_applicator = {
+	.apply = tftp_apply_settings,
+};